Environmental Engineering Reference
In-Depth Information
3.2 basiC PuMPing CalCulaTions
Calculations, calculations, calculations, and more calculations!
Yes, calculations; indeed, we cannot get away from them—not in waste-
water treatment and collection operations, licensure certification exam-
inations, nor in real life. Basic calculations are a fact of life that the
water/wastewater maintenance operator must accept and should learn
well enough to use as required to operate a water/wastewater facility
correctly. The following sections address the basic calculations used
frequently in water hydraulic and pumping applications. The basic cal-
culations that water and wastewater maintenance operators may be
required to know for operational and certification purposes are also
discussed. In addition, calculations for pump specific speed, suction
specific speed, and affinity, among other advanced calculations, are also
covered in this section, although at a higher technical level.
3.2.1 velocity of a fluid through a Pipeline
The speed or velocity of a fluid flowing through a channel or pipeline
is related to the cross-sectional area of the pipeline and the quantity of
water moving through the line; for example, if the diameter of a pipeline
is reduced, then the velocity of the water in the line must increase to
allow the same amount of water to pass through the line:
Flow ()(cfs)
Cross-Sect
q
Velocity ()(fps)
v
=
(3.1)
2
ionalArea( ) (ft )
a
Example 3.1
Problem:
If the flow through a 2-ft-diameter pipe is 9 MGD, what is the
velocity?
Solution:
9MGD
×
1.55 cfs/MGD
=
14 cfs
3.14 ft
Velocity
=
2
=
4.5fps (rounded)
0.785
××
2ft2ft
Example 3.2
Problem:
If the same 9-MGD flow used in Example 3.1 is transferred to a
pipe with a 1-ft diameter, what would the velocity be?
Solution:
9MGD
×
1.55 cfs/MGD
=
14 cfs
0.785ft
Velocity
=
2
=
17.8 fps(rounded)
0.785
××
1ft1ft
